Research on whether patient psychological and personality variables can predict placebo response has been inconclusive and contradictory. The problem in identifying and validating these patient variables may stem from the methods used to assess them. In particular, prior investigations have assessed these variables in isolation from the patient-practitioner relationship, often via self-report questionnaires at baseline. It is likely, however, that the important patient variables that influence placebo response are not to be found in global measures of personality in general nor in attitude measures collected just prior to treatment, but rather in specific measures of patient variables as they manifest themselves in the clinical encounter between a particular patient and a particular practitioner at a particular point in time. In response to Program Announcement #PA-02-094 "Ancillary Studies on Control Groups in Clinical Trials," we propose studying these patient variables by using an existing patient population from an NIH-funded project entitled, "Enhancing the Placebo Effect in Irritable Bowel Syndrome" (R01 AT 1414-2, Dr. Ted Kaptchuk, PI). We propose using the Psychotherapy Process Q-Set (PQS), a well-validated measure of interpersonal process in psychotherapy, and applying it to a new domain-the clinical encounter between patient and practitioner in the setting of a somatic illness. Our main hypothesis is that patient variables when measured in the context of a clinical encounter will predict placebo response. This research has important implications both for researchers-who typically strive to reduce placebo effects-and for clinicians who usually seek to maximize non-specific placebo responses so as to increase their patients' overall response to the active treatment. This is an innovative attempt to integrate cutting edge psychotherapy research methodology into the study of the placebo response.